# Mutual Inductance analysis circuit

Discussion in 'Homework Help' started by full, Sep 13, 2014.

1. ### full Thread Starter Member

May 3, 2014
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Hello everyone,

Actually I not understand the Mutual Inductance analysis circuit, but I do one problem ....

Please can you check my solution true or wrong,

thanks,

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2. ### t_n_k AAC Fanatic!

Mar 6, 2009
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I don't see how the mutual inductance can be 1H when with perfect coupling it can't be greater than 0.3536H.

$M=k \sqrt{L_1L_2}$

3. ### full Thread Starter Member

May 3, 2014
225
2

but I not understand in this video how do mutual inductance analysis

how I know the mutual inductance is positive or negative ?

but I do my problem form this key:

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Last edited: Oct 31, 2014
4. ### t_n_k AAC Fanatic!

Mar 6, 2009
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I fail to see the the point of trying to solve a problem based on a false premise.

5. ### full Thread Starter Member

May 3, 2014
225
2
how I know the mutual inductance is po
ok sir, I will do another problem

6. ### full Thread Starter Member

May 3, 2014
225
2
I do new problem , please check loops 1&2 :

thanks,

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7. ### t_n_k AAC Fanatic!

Mar 6, 2009
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You do have a problem with the dot convention.

My approach is simply to say:
Current flowing into a dot on a winding produces a positive mutually induced emf at the dot on mutually coupled windings.

So for your first mesh equation:

$-800+200I_1+j480I_1+j360 (I_2-I_1)+j720 (I_1-I_2)-j360I_1=0$

8. ### full Thread Starter Member

May 3, 2014
225
2
but I think in rule of thumb on dot convention ( flow into*flow out =>negative)

what is meaning emf?

thanks,

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9. ### t_n_k AAC Fanatic!

Mar 6, 2009
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In reality you can adopt whatever convention you like as long as you are consistent with the application of the "rules".
The meaning of emf - electro-motive force.

10. ### full Thread Starter Member

May 3, 2014
225
2
sir, first of all, what is the meaning of the "dot"? (Mutual Inductance )true?

and how can be calculated? thanks for your nice support

Last edited: Sep 14, 2014
11. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
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The dot indicates there is magnetic flux coupling between one or more inductors as represented in a schematic diagram.
As shown in your schematics the mutual inductance between the various inductors is indicated by the arrow(s) with an annotated value in units of inductance. Sometimes only the coefficient of coupling is shown and one then apples the formula for mutual inductance to determine the actual value.
The location of the dot indicates the mutually induced voltage (emf) polarity in an inductor for a given condition (voltage or current) in a another mutually coupled inductance.

12. ### t_n_k AAC Fanatic!

Mar 6, 2009
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My solution attached.

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13. ### JoeJester AAC Fanatic!

Apr 26, 2005
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Interesting. I tended to believe the dots represented phasing, so you can tell whether or not the mutual inductance is aiding or opposing.

Jan 29, 2010
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15. ### full Thread Starter Member

May 3, 2014
225
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Thank you sir ,

16. ### The Electrician AAC Fanatic!

Oct 9, 2007
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Shouldn't that be two or more inductors?

I remember a post in a newsgroup from some years ago concerning the situation where 3 inductors were coupled. A Spice simulation complained that the various mutual inductances were not physically realizable. Somebody posted a reference from an IEEE journal article where it was explained that if the matrix of self and mutual inductances were formed, it had to be positive definite to be realizable.

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17. ### full Thread Starter Member

May 3, 2014
225
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I am do this problem 3 time same answer :
where is wrong?

thanks

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Last edited: Oct 29, 2014
18. ### t_n_k AAC Fanatic!

Mar 6, 2009
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The problem is with mesh 1 equation. Specifically, the term -j2*I1 should be positive sign rather than negative.

full likes this.

May 3, 2014
225
2
obs

thanks sir

20. ### full Thread Starter Member

May 3, 2014
225
2
I am do this problem in ideal transformer :
where is wrong?

thanks

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Last edited: Oct 31, 2014